A large number of organoselenium and organotellurium compounds are known in the literature. For comprehensive reviews of organic selenium and tellurium chemistry, see Organic Selenium Compounds: Their Chemistry and Biology, D. L. Klayman and W. H. H. Gunther, Ed., Wiley, New York, 1973, and K. J. Ingolic, The Organic Chemistry of Tellurium, Gordon and Breach, New York, 1974. Methods of preparing organic tellurides and selenides have involved the formation of alkali metal chalcogen reagents in liquid ammonia. See e.g. Grushkin et al., U.S. Pat. No. 3,965,049. A direct two-step process for synthesis of aromatic molecular and supramolecular organic tellurides, ditellurides and selenides has been described in which an alkali metal chalcogenide reagent is generated without the use of liquid ammonia. Sandman et al., U.S. patent applications Ser. No. 506,690 and Ser. No. 507,156.
The first step is preparation of an alkali metal chalcogenide reagent in an aprotic solvent directly from elemental chalcogen and an alkali metal. An alkali metal is reacted with elemental selenium or tellurium in dipolar aprotic solvents such as dimethylformamide (DMF), N-methylpyrrolidinone (NMP) and hexamethylphosphoramide (HMPA) in 1:1 or 2:1 ratios to give alkali metal chalcogenide reagents M.sub.2 Ch.sub.2 and M.sub.2 Ch (wherein M=Na, K, Li and Ch=Se, Te). The second step involves direct thermal reaction of an aromatic halide with the alkali chalcogenide reagent formed in the first step. The facility of these reactions is noteworthy because nucleophilic substitution in aromatic halides usually requires either strenuous conditions or aromatic substrates activated by electron attracting substituents.
Alkali chalcogenide reagents prepared as described above have proven useful for direct synthesis of both new and previous reported molecular and polymeric ditellurides, tellurides and selenides. See Sandman et al., U.S. patent applications Ser. No. 506,690 and Ser. No. 507,156.
Alkali chalcogenide reagents may also be prepared by reacting a chalcogen with an alkali metal trialkylborohydride in tetrahydrofuran. See Gladysz, J. A. et al. J. Org. Chem. 43, 1204-1208 (1978). Alkali metal chalcogenide reagents prepared in this manner have been reacted with alkyl and acyl halides and transition metal systems. For example, Gladysz and coworkers formed alkali metal selenide and diselenide reagents from selenium and lithium trialkylborohydride and synthesized molecular dialkyl selenides and diselenides therefrom. Bender et al. describe a reaction of chloromethyltellurolalkynes with dilithium telluride reagent prepared from tellurium and lithium triethylborohydride to form 1,3-ditelluroles. Tetrahedron Lett. 23, 1531 (1982).
A lithium diselenide reagent formed from selenium and lithium triethylborohydride has been used to synthesize bis-aryl diselenides. Battistoni, P. et al. Gazz. Chim. Ital. 111, 505 (1981). However, the aryl halide reactants were O-chloronitrobenzenes, aromatic compounds which have a strong electron withdrawing ring substituent in addition to the halogen atom, namely the nitro (--NO.sub.2) group. This strong electron withdrawing group activates the compound toward nucleophilic substitution.